PET Scan - What to Expect

A positron emission tomography (PET) scan is a diagnostic examination used to detect cancer, determine the stage of cancer, and evaluate the effectiveness of cancer treatments, such as chemotherapy or radiation therapy.

In a PET scan, radioactive sugar molecules are injected into the body. Cancer cells absorb sugar more quickly than normal cells, so they light up on the PET scan. A PET scan is often used to complement information gathered from a computed tomography (CT) scan, magnetic resonance imaging (MRI), or physical examination. An integrated PET-CT scan collects images from both PET and CT scans at the same time and superimposes the images.

The medical team

A PET scan is performed by a radiologist or technologist who specializes in nuclear medicine. A radiologist is a medical doctor who performs and interprets imaging tests to diagnose disease. A nuclear medicine technologist is specially trained to operate PET scanners and in other procedures involving radioactive materials.

Questions to ask your doctor

Before having a PET scan, consider asking your doctor the following questions:

  • Who will perform the PET scan?
  • What will happen during the PET scan?
  • How long will the procedure take?
  • Are there risks of having a PET scan?
  • If I am pregnant or breast-feeding, should I have this test?
  • Will I need to avoid any activities after the PET scan?
  • Do I need to bring any of my other radiologic images (for example, MRI, CT) to my appointment?
  • When will I learn the results?
  • Who will explain the results to me?
  • What further tests will be necessary if the test results indicate cancer?

Preparing for the procedure

When you schedule the examination, you will get detailed instructions on how to prepare for the PET scan. Tell your doctor or nurse about all medications you are taking, as well as any drug allergies or other medical conditions you have and whether you should take your regular medications that day.

You will be asked to sign a consent form that states you understand the benefits and risks of the PET scan and agree to have the test done. Talk with your doctor about any concerns you have about the PET scan.

You will be instructed to not eat or drink anything except water for several hours prior to your scan. You may be told to drink a significant amount of water because the radioactive sugar is cleared through the urine.

Wear loose, comfortable clothing. PET scanners need to be kept cool, so the examination room may feel chilly. You will be asked to remove any jewelry.

Some facilities allow patients to listen to music during their scans. You may want to ask if you can bring your own music.

During the procedure

When you arrive for your PET scan, the radiologist or a nurse will administer the radioactive sugar molecules through an injection into a vein (called intravenous, or IV injection). The injection will feel like a pinprick, but the radioactive material will not create any sensation in your body.

After the injection, the radioactive substance will take 30 to 90 minutes to reach the tissues to be scanned. During that time, you will need to lie quietly without moving or talking; too much motion can disrupt the accumulation of the sugar molecules.

When your body is ready for the scan, you will be moved to the examination room. You will lie on a cushioned exam table outside of the PET scanner, which resembles a large donut. You will not need to remove any clothing.

The scanning itself takes approximately 30 to 60 minutes. The table will slide slowly through the large hole in the center about six times during the test. The PET scanner does not make a lot of noise, you will need to lie still for the entire scan, and you will not be enclosed in the scanner at any time. If you are having a PET-CT scan, the procedure will seem very similar.

After the procedure

You can expect to resume your normal activities immediately after your PET scan. You will be advised to drink several glasses of water to flush the radioactive material out of your body, though there are no side effects from the radiation.